The present invention relates to a method for fabricating a semiconductor device, and more particularly to a method for forming storage node contacts in a semiconductor device.
In a semiconductor memory device including capacitors, such as a dynamic random access memory (DRAM), bit lines are first formed and then the capacitors are formed, so as to increase the effective dimensions of the capacitors. Storage node contacts are formed after the bit lines to electrically connect impurity regions (e.g., source/drain regions) of transistors and storage nodes of the capacitors.
Now, a process for forming storage node contacts will be described. First, landing plug contacts (LPCs) are formed on a semiconductor substrate by forming landing plug contact holes by selectively removing a first dielectric layer from the semiconductor substrate and filling the landing plug contact holes with a conductive layer. The landing plug contacts serve to electrically connect impurity regions of the semiconductor substrate and storage node contacts. Thereafter, storage node contact holes are formed by forming a second dielectric layer on the LPCs and the first dielectric layer and selectively etching the second dielectric layer. Then, the storage node contact holes are filled with a conductive layer. Thereby, the storage node contacts are obtained.
In the above process, the etching of the second dielectric layer for forming the storage node contact holes is performed using a hard mask layer. That is, the hard mask layer is formed on the second dielectric layer, and the second dielectric layer is etched using the hard mask layer as an etching barrier layer. Generally, a polysilicon layer or a nitride layer is used as the hard mask layer. If necessary, a nitride layer containing a hydrogen component may be used as the hard mask layer. The polysilicon layer causes alignment keys not to be optically visible, thus requiring an additional step for alignment. The nitride layer deteriorates the stability of the device due to stress to a lower layer, and causes defects of the device. The nitride layer containing the hydrogen component allows alignment keys to be optically visible so as to omit any additional step for alignment, and alleviates the stress applied to the lower layer. However, the nitride layer containing the hydrogen component causes the hydrogen component to be diffused into the second dielectric layer, and deteriorates electrical characteristics of the device.